The present invention relates to apparatus and method for actively reducing vibration and/or noise in which a reduction control against a periodic noise or periodic vibration is executed using an adaptive digital filter whose weight coefficients (filter coefficients) are updated in accordance with an adaptive algorithm. The present invention specifically relates to the actively vibration and/or noise reducing apparatus and method in which a divergence of the reduction control for higher order harmonics of the periodic vibration or noise can easily be determined without failure.
A Japanese Patent Application First Publication Heisei (JP-A1-) 7-239690 published on Sep. 12, 1995 exemplifies a previously proposed actively vibration and/or noise reducing apparatus.
In the previously proposed actively vibration and/or noise reducing apparatus disclosed in the above-identified Japanese Patent Application Publication, a control sound or a control vibration is interfered against the periodic noise transmitted from a noise source such as a vehicular engine into a passenger compartment or the periodic vibration propagated onto a vehicle body from a periodic vibration source such as the vehicular engine so as to reduce the noise and/or the vibration. In addition, in a controller of the previously proposed vibration and/or noise reducing apparatus, a reference signal representing a developed condition of the periodic noise or the periodic vibration is filtered through an adaptive digital filter so as to generate and output a drive signal to drive a control sound source or a control vibration source and filter coefficients of the adaptive digital filter are sequentially updated in accordance with an adaptive algorithm.
Since a synchronous-type Filtered-X LMS (Least Mean Square) algorithm is used as the adaptive algorithm described above, a higher order divergence which occurs when the above-described Filtered-X LMS algorithm is applied as the adaptive algorithm is determined and an appropriate countermeasure against the occurrence of the higher order divergence is taken.
Specifically, a local maximum value e1MAX and a local minimum value e1MIN of the residual vibration signal, the residual noise signal or drive signal within one period of the reference signal x is searched and a controller determines whether the divergence of the control occurs on the basis of an appearance interval .DELTA.t1 between the local maximum value e1MAX and the local minimum value e1MIN and a difference .DELTA. E1 between these maximum and minimum values. In other words, under such a situation that the control to reduce the periodic noise or periodic vibration is normally executed without divergence, the period of the residual noise signal, residual vibration signal, or the drive signal should coincide with the period of the reference signal. On the other hand, under such a situation that the control tends to progressively be diverged in higher orders, higher order signal components than the reference signal appear on the residual noise signal, residual vibration signal, or drive signal. The higher signal components becomes larger as the tendency of the higher order divergence becomes stronger. Hence, a presence or absence of the higher order divergence of the control and a magnitude of the divergence can be determined depending upon the appearance interval and difference between the local maximum value and local minimum value of the residual noise signal, of the residual vibration signal, or of the drive signal.
Since, in the previously proposed actively vibration and/or noise reducing apparatus disclosed in the above-identified Japanese Patent Application Publication, the high order divergence of the control can be determined without a frequency analysis of each signal by means of a FFT (Fast Fourier Transform), a remarkable increase in an arithmetic operation load on an arithmetic operation and processing unit is not resulted.
The previously proposed apparatus for actively reducing vibration and/or noise can determine the presence or absence of the divergence of the control and magnitude of the divergence and can reduce the arithmetic operation load as compared with the analysis using the FFT. However, it is necessary to execute various types of arithmetic operation processes such as a search (retrieving) processing of each of the local maximum value and local minimum value, the arithmetic processing of the appearance interval and difference between the local maximum and local minimum values, and the determination processing of the divergence. Hence, an expensive microprocessor having a high arithmetic processing capability needs to be used in order to actually perform the vibration and/or noise reducing control in parallel to performing the divergence determination processing.
In other words, an industry has demanded a further simplification of arithmetic processing required to determine the higher order divergence of the control.